Carrier pipes such as those used in municipal water systems often encounter significant dynamic and static loads, corrosive elements, vibrations, and other destructive factors associated with aggressive environments such as under roads, railway rights-of-way, and other underground locations. Carrier pipe which is not surrounded by a protective, larger diameter casing is therefore generally more prone to failure, leakage-producing deformation and degradation over time than protected carrier pipe. However, carrier pipe simply placed in a casing without proper spacing from the casing suffers galvanic and chemical reactions and exposure to the carrier pipe underside due to contact between the carrier pipe and the spacing.
Conventional casing spacers include the "band and boards" systems in which suitably sized lumber may be banded about desired portions of the carrier pipe before it is placed in the casing. The lumber tends to degrade over time, however, and may be destroyed or inadvertently displaced during installation. Such wooden spacers also typically result in high labor costs, because they require generally three to six workers and considerable coordination and planning to install. Physically, they are easily dislodged and place an uneven load on the pipe unless the boards are spaced symmetrically. They may rot and allow settlement, or they can, on the other hand, swell and subject carrier pipe joints to breakage. They do not provide complete assurance of electrical insulation, and chemically, they allow bacteria and differential oxygen concentration corrosion.
A more recent approach in view of these problems has been the use of specially designed casing spacers which feature a preformed steel or plastic band for encircling the carrier pipe, on which glass reinforced plastic runners are formed, generally in a "star" configuration when viewed in cross section. Installation instructions for such spacers address a problem often faced also with band and boards approaches: the spacers do not sufficiently protect the joints. Instead, they are disposed between non-joint portions of the carrier pipe and the casing spacer so that the joint portions are cantilevered from the points supported by the casing spacers. This more recent approach therefore does not allow the pipe joint itself to be positioned with respect to the casing so that the joint may flex without being subjected to undue forces. The inventor has additionally found that such spacers are subject to inadvertent destruction and deformation as the carrier pipe is placed in the casing, because of the relatively lightweight construction when compared with the heavier carrier pipe. Furthermore, such spacers present significant distribution and inventory problems for suppliers and distributors since multiple sizes and configurations must be carried to accommodate different sizes and types of carrier pipe and casings.